Products made from a fibrous web are used for a variety of purposes. For example, paper towels, facial tissues, toilet tissues, napkins, and the like are in constant use in modern industrialized societies. The large demand for such paper products has created a demand for improved versions of the products. If the paper products such as paper towels, facial tissues, napkins, toilet tissues, mop heads, and the like are to perform their intended tasks and to find wide acceptance, they must possess certain physical characteristics.
Among the more important of these characteristics are strength, softness, and absorbency. Strength is the ability of a paper web to retain its physical integrity during use. Softness is the pleasing tactile sensation consumers perceive when they use the paper for its intended purposes. Absorbency is the characteristic of the paper that allows the paper to take up and retain fluids, particularly water and aqueous solutions and suspensions. Important not only is the absolute quantity of fluid a given amount of paper will hold, but also the rate at which the paper will absorb the fluid.
Through-air drying papermaking belts comprising a reinforcing member and a resinous framework, and/or fibrous webs made using these belts are known and described, for example, in the following commonly assigned U.S. Pat. No. 4,514,345, issued Apr. 30, 1985 to Johnson et al.; U.S. Pat. No. 4,637,859 issued Jan. 20, 1987 to Trokhan; and U.S. Pat. No. 6,660,129 issued Dec. 9, 2003 to Cabell et al.
In the aforementioned belts of prior art the resinous framework is joined to the fluid-permeable reinforcing member (such as, for example, a woven structure, or a felt). The resinous framework may be continuous, semi-continuous, comprise a plurality of discrete protuberances, or any combination thereof. The resinous framework extends outwardly from the reinforcing member to form a web-side of the belt (i. e., the surface upon which the paper web is disposed during a papermaking process), a backside opposite to the web-side, and deflection conduits extending therebetween. The deflection conduits provide spaces into which papermaking fibers deflect under application of a pressure differential during a papermaking process. The terms “papermaking belt,” and “forming member,” may be used herein interchangeably.
Paper produced on the papermaking belts disclosed in the aforementioned patents are generally characterized by having at least two physically distinct regions: a region having a first elevation and typically having a relatively high density, and a region extending from the first region to a second elevation and typically having a relatively low density. This is because papermaking belts on which the paper is produced generally have two distinct regions at two distinct elevations, a first region at a first elevation associated with the resinous framework, and a second region at a second elevation associated with the woven (or felt) reinforcing member. The first region is typically formed from the fibers that have not been deflected into the deflection conduits, and the second region is typically formed from the fibers deflected into the deflection conduits of the papermaking belt. The papers made using the belts having a continuous resinous framework and a plurality of discrete deflection conduits dispersed therethrough comprise a continuous high-density network region and a plurality of discrete low-density pillows (or domes), dispersed throughout, separated by, and extending from the network region. The continuous high-density network region is designed primarily to provide strength, while the plurality of the low-density pillows is designed primarily to provide softness and absorbency. Such belts have been used to produce commercially successful products, such as, for example, BOUNTY® paper towels, CHARMIN® toilet tissue, and PUFFS® facial tissue, all produced and sold by The Procter & Gamble Co.
Certain aspects of absorbency of a fibrous structure, as well as its ability to clean more effectively, are highly dependent on its three-dimensional surface area. By three-dimensional surface area is meant the surface area that includes out-of-plane three-dimensionality such that a sheet of fibrous structure of a given overall two-dimensional size has a three-dimensional surface area greater than its two-dimensional calculated area. Attempts have been made to increase the three-dimensional surface area by increasing the number and placement of different elevations of a papermaking belt. That is, for a given fibrous web, the greater the web's three-dimensional surface area the higher the web's absorbency and cleaning performance. In the three-dimensional structured webs made on the aforementioned papermaking belts, the low-density pillows and the transition areas between the pillows and the relatively high density regions, dispersed throughout the web, increase the web's three-dimensional surface area, thereby increasing the web's absorbency. However, increasing the web's surface area by increasing the area comprising the relatively low-density pillows would result in decreasing the web's area comprising the relatively high-density network area that imparts the strength.
Attempts to increase absorbency and cleaning performance of absorbent paper products by increasing the three-dimensional surface area include using two layers of a resinous framework of the forming member. One example of using two layers of a resinous framework is shown in U.S. Pat. No. 6,660,129 B1, issued Dec. 9, 2003 to Cabell et al. Cabell et al. discloses a fibrous structure having at least a first region defining a first plane and having a first elevation, and a second region outwardly extending from the first plane to define a second elevation, wherein the second region comprises a plurality of fibrous pillows. Due to the nature of the resinous framework on the forming member described in Cabell et al., one feature of a fibrous structure made thereon is fibrous cantilever portions laterally extending at a second elevation. This is believed to be because of the nature of the process of producing the resinous framework of Cabell et al., which includes randomly dispersed cantilevered portions of the second layer of the resinous framework of Cabell et al. It is believed that the cantilevered portions can be weakened and fail during prolonged use of the belt, and, as well, fail to produce increased surface area in the finished paper of a type not requiring the cantilevered portions.
There is a continuing unaddressed need for a papermaking belt that can produce fibrous structures having greater absorbency and cleaning performance, particularly cleaning of soils and other solids, due to increased three-dimensional surface area.
Additionally, there is a continuing unaddressed need for a papermaking belt that can produce fibrous structures having distinct three-dimensional features in discrete planes, but which are not cantilevered.
Additionally, there is a continuing unaddressed need for a method for making a papermaking belt having a multi-stage, three-dimensional structure in a single pass.
Further, there is an unaddressed need for a three-dimensional mask that can produce a papermaking belt that can produce fibrous structures having distinct three-dimensional features in discrete planes, but which are not cantilevered.